Processing Type 1: All images were flattened with a corresponding image of white surface. The flats were smoothed by blurring with a gaussian-like filter, normalized to have a maximum value of unity and divided into the corresponding spectral image.

Processing Type 2: A linear contrast stretch applied to the 16-bit single-wavelength images. The black and white values were set 3 standard deviations away from the average value. The values beyond 3 standard deviations were clipped to black or white.